Optical access networks are these days a prominent solution, for transmitting data from an optical line terminal to multiple optical network units. The optical line terminal is located at a central office, wherein the optical line terminal acts as an interface between the optical access network and a core network for data transmission. The optical line terminal receives data from the core network and transmits this in downstream direction towards the optical network units (ONU), to which customers may connect their equipment for data transmission. The downstream signal generated by the optical line terminal is transmitted into an optical feeder fiber, to which a remote node is connected. This remote node splits the downstream signal onto different optical branches, to which the different optical network units are connected.
One solution for transmitting different data streams assigned to different optical network units is, to allocate within the downstream signal for each optical network unit one or more time slots, within which multiple data bits of the data stream assigned to the respective optical network unit are placed by the optical line terminal. In such a solution, the respective optical network unit needs to receive within such a time slot data at a certain data rate, while during other time slots, assigned to other optical network units, the respective optical network unit does not need to receive data at any data rate. This implies, that the optical network unit has to be able to receive data within the designated time slot at a data rate, which is higher than the overall average data rate, by which the assigned data stream is transmitted from the optical line terminal to the respective optical network unit.
An alternative solution, within which an optical network unit may receive data from an optical line terminal at a constant data rate, is provided by a bit-interleaving protocol of a so-called bit-interleaving passive optical network (BIPON). In such a BIPON, the bit data of different data streams assigned to different ONUs are interleaved within a global frame, such that the resulting data rate of each data stream for each ONU has a respective constant value. A global frame may contain for example up to 8*19,200 Bytes=153,600 Bytes, which is equal to 1,228,800 Bits. The bits of one specific data stream are placed within the global frame equidistantly to each other, which leads to a resulting constant data rate for this data stream. A global frame is then followed by further successive global frames for an ongoing data transmission.
The data rate for a specific data stream is defined by the number of bit positions, by which the bits of this data stream are spaced, assuming a given time duration of the global frame. By placing the bits of different data streams with different respective equidistant spacing within the global frame, different data rates are realized. The advantage of a BIPON is, that an ONU needs to receive data not at the overall data rate provided by the global frame, but at a lower data rate, which is defined by the time duration of the global frame and the rate, at which the bits of this specific data stream of this ONU are placed inside the global frame. This allows for operation of an ONU at a lower data rate than the maximum data rate realized by the successive global frames of a BIPON.
Even furthermore, by changing the rate at which data bits of a specific data stream are placed inside the global frame, a changed data rate is thus realized for the associated optical network unit.
Within a BIPON, an optical line terminal thus has to perform reception of different data streams assigned to different optical network units, and also has to perform a proper bit-interleaving of the bits of the different data streams into successive global frames, such that different pre-determined data rates are realized for the respective different optical network units.